Subwoofers, Impedance, HDMI Audio

Funny, I Was Just Talking About This
Is there a downside to using speakers with built-in subwoofers? I have a pair of Mirage OM-5 speakers with built-in subs, a Rotel RSP 1098 preamp, and a 5- and 2-channel amp to power seven speakers, all Mirage.

John Seabrook

I talk about this very subject in my latest Home Theater Geeks podcast with speaker designer Sandy Gross. The Triton speakers he designed for his new company, GoldenEar Technology, include built-in powered subs, an approach he advocates because it lets him blend the sound of the sub with the rest of the speaker. He also says that putting two subs in a room helps smooth out room modes.

It's true that multiple subwoofers can smooth out room modes, but I maintain that the ideal location for a sub is not necessarily the same as the ideal location for any of the main speakers, because the placement of the sub dramatically affects how it excites the room modes. Therefore, I prefer to have one or more separate subs. Granted, this means it's up to the user to blend the sound of the sub with the sound of the main speakers, and that blend may not be as good as it is from a speaker with a built-in sub, but I'd rather have the flexibility to place the sub(s) where they produce the smoothest bass.

Impy Dance
Up until a few months ago, I had been blessedly ignorant of the different amounts of power drawn by 4Ω versus 8Ω speakers, but a couple of Home Theater reviews have recently talked about great receivers that may not be acceptable for "power hog" speakers. I presume 4Ω speakers are the power hogs to which those articles referred, right? After reading those articles, I took a closer look at my M&K 750s and learned that they are, in fact, 4Ω speakers.

Now, my Onkyo receiver seems to be approaching the ghost-giving stage, and I'm not sure if its impending death is related to the 4Ω speakers I errantly selected. In any event, it looks like I will get to—er, that is, have to—shop for a new receiver to drive my M&Ks, and I'm wondering what are the minimum specs I should be looking at. The Onkyo TX-SR608 got a great review from Home Theater, but I'm betting it's a bit weak for my speakers, isn't it? Am I stuck looking at the Onkyo TX-NR5008 or A/V receivers in that class for this type of speaker? My pocketbook and my wife really want to know.

Scott Miller

Low-impedance speakers are indeed power hogs—they draw more power from an amplifier than higher-impedance models. Thus, it's a fairly safe bet that your speakers have been asking a lot from your current AVR, probably more than it's designed to give, which could be why it's approaching the ghost-giving stage.

When shopping for an AVR, the important spec in this regard is the impedance it's designed to drive. Most AVRs, especially those at the lower end of the price scale, are not designed to drive speakers with an impedance of 4Ω or lower, so you're right to be looking at higher-end models, some of which have a switch that configures the output for different impedances.

But even some high-priced models are not designed to power 4Ω speakers—ultimately, you have to determine this from the specs. Unfortunately, the specs don't always reveal this information, which means finding a knowledgeable dealer or talking to the manufacturer's customer-service department (good luck with that!). Another option is looking at the owner's manual, which is often available online.

The North American version of the Onkyo TX-SR608 is rated for speakers between 6 and 16Ω, info I found in the manual, not the specs. The TX-NR5008 can drive loads from 4 to 16Ω, and it has a switch in the menu system to select the best value for your speakers.

Prima Schema
Which connection scheme will give me the best audio, HDMI to the TV and optical to A/V receiver, or HDMI to AVR?

Dale Hutchinson

Without question, you'll get the best audio from a Blu-ray player by connecting its HDMI output to the AVR, then HDMI from the AVR to the TV for video. HDMI can carry the new lossless audio formats, DTS-HD Master Audio and Dolby TrueHD, while an optical connection cannot. Of course, the Blu-ray disc must include a soundtrack in one of these formats, but most do.

With most other source devices—DVD players, HDTV receivers, etc.—HDMI is not better or worse for audio than an optical connection, because these devices send audio in the older Dolby Digital or DTS formats, which optical can carry just fine. Still, to keep it simple, I'd connect everything to the AVR via HDMI, and a single HDMI cable to the TV.

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1ace007's picture

Scott, I was wondering what is the brand and model of the speaker pictured above. It is a sharp looking speaker!

Orup70's picture

Not Scott, but they are the Mirage OM-5 in the question. I've had a pair of them since 2001 and they are both good looking and has a great sound.

I've upgraded since a year ago to a pair of Paradigm S8 and a separate sub woofer (Paradigm Sub 25) but the Mirage OM-5 were really good. The strange thing with the Mirage speakers is that they had a 250 W sub woofer built-in that's driven by the normal high level speaker signal. So you don't even know they have a sub woofer, except for the mains cord going into each speaker. They are almost flat down to 25 Hz and has a great bass.

I still have my OM 5:s in the basement, partly because I still like them and partly because the market for old HiFi equipment is not that great where I live.

1ace007's picture

Okay, they're the ones the reader mentioned (of course)in his question. I also have Paradigm speakers and I really like them. I have a pair of monitor 9's that I upgraded to from a pair of Titans and a PDR10 SW. I still have the PDR 10 but I think I need a larger Sub to compliment the Mon. 9's better. I hope to upgrade to a PDR12 or greater if they're still available when this economy we're in turns around.

Clayton72's picture

I have an Anthem AVM30. It doesn't have HDMI, so no luck there for audio. I've been pluging all the HDMI's into the TV and then using optical from the TV to get sound to the Anthem. Is there a better way?

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